The present invention relates to a needle lift estimation system of a common-rail injector used for a high-speed direct injection system of a diesel engine, and more particularly, to a needle lift estimation system of a common-rail injector for estimating needle lift based on measured current and solenoid voltage of the common-rail injector.
Diesel fuel injection systems typically utilize a cam-driven apparatus in order to generate injection pressure, where injection pressure increases and accordingly an amount of injected fuel also increases as the rotating speed of the cam increases. However, such a cam-driven apparatus is generally reliable only when injection pressure is somewhat low.
In addition, use of a high-speed direct injection (HSDI) engine is becoming more prevalent for passenger vehicles as well as commercial vehicles. The HSDI engine consumes less fuel and generates more power than an indirect fuel injection engine. In a common-rail injection apparatus used for such an HSDI engine, generation of injection pressure and injection of the pressurized fuel are totally separate. For separation of the two functions, a high-pressure accumulator or rail is used to maintain high fuel pressure.
In such a common-rail injection apparatus, a nozzle injector equipped with a solenoid is disposed at a position where a nozzle holder was disposed previously. High fuel pressure is generated by a radial piston pump for which rotation speed is easily controlled separately from engine revolution speed, within a predetermined range. This system provides more freedom for designing fuel injection, and accordingly the combustion mechanism, because it enables separate design and assembly of fuel pressure generating devices and fuel injection devices.
An injector used in the common-rail injection system utilizes a high-speed and high-pressure solenoid. It regulates injection timing, injection period, and injection ratio using electrical forces of the solenoid. Precise control of injection timing, injection period, and injection ratio make it possible to decrease the amount of exhaust gases output and increase engine efficiency. On the basis of precise data on needle lift, injection timing, injection period, and injection ratio can be precisely determined.
For precise estimation of the needle lift, an eddy-current-type sensor has been used. In the estimation method using the eddy-current-type sensor, displacement of a coil in the magnetic field that moves in response to the displacement of the needle is changed to a specific electrical signal, and the needle lift is estimated from the electrical signal. There are also estimation methods using an optical sensor utilizing an optical fiber, estimation methods using ultra-sonic waves, and a contacting-type estimation method. Such methods commonly estimate the needle lift using a sensor.
For engine control, various kinds of engine operating parameters are required, and correspondingly, various kinds of sensors are needed for detecting the various kinds of engine operating parameters. These sensors add to the cost of producing the engine, and in particular, the sensor for detecting the needle lift for operating the common-rail injector significantly increases manufacturing cost.
The present invention provides a needle lift estimation system for a common-rail injector and a method thereof, in which the needle lift can be estimated on the basis of the solenoid voltage and measured current without various sensors.
In a preferred embodiment of the present invention, a needle lift estimation method comprises measuring a current that is supplied to a solenoid, estimating an armature lift and an armature speed on the basis of the current supplied to the solenoid, and estimating a needle lift from a state equation including the measured solenoid current, the estimated armature lift, and the estimated armature speed as state variables.
In another preferred embodiment of the present invention, a needle lift estimation system comprises an observer that measures a solenoid current and estimates an armature lift and an armature speed, wherein the armature regulates the pressure of the pressure-control chamber. The armature moves up and down by the magnetic force of the solenoid coil, and a needle is operated in response to the movement of the armature such that the needle opens or closes an injection hole.